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analysis indicate that the coat protein of MGNNV has two domains resem-
bling those of tomato bushy stunt virus and Norwalk virus, rather than
the expected single-domain coat protein of insect nodaviruses. The analysis
implies that residues 83 to 216 fold as a β-sandwich that forms the inner
shell of the
T
= 3 capsid and residues 217 to 308 form the trimeric surface
protrusions observed in the cryoEM map. Deleting N- and C-termini
revealed different impacts on VLP formation. Deletion of 35 or 52 residues
at the N-terminus completely ruined the VLP assembly, presumably due to
removal of positively charged residues for binding RNAs. When deletions
were restricted to 4, 16, or 25 N-terminal residues, the assembly of VLPs
remained. The ability of VLP formation diminished when 4 to 11 C-terminal
residues were deleted. The termini that can be deleted without seriously
destructing the VLPs are 25 and 3 residues at N- and C-termini, respectively.
The recombinant VLPs block attachment of native virus to the surface of
cultured fish cells, thereby blocking infection by the native virus.
Introduction
After five years of observations in the Kyushu hatchery, Mori
et al
.
published in 1992 the new virus, a spherical particle from infected lar-
val striped jack (
Pseudocaranx dentex
), and classified it as a nodavirus
by its bipartite geneme of ~1.5 kb and ~3 kb.
1
Using cell-free extract
of rabbit reticulocytes, three bands of proteins were found, which
were 40 kDa, 42 kDa, and 100 kDa. The protein of 42 kDa is capsid,
while RNA polymerase is 100 kDa; 40 kDa was presumed as a trun-
cated capsid protein. The virus particles were mainly found in brain
and retinal cells, with a diameter of 25-30 nm and with non-envelope
icosahedral shape. This is the first
Betanovirus
identification that was
once mistaken as picornavirus.
Piscine nodaviruses were officially classified in the genus
Betano-
davirus
by ICV in 2001, although Asian scientists once rather named
it as piscinodavirus. All of the literature mentioned in this paper can be
referenced to the review by Munday
et al
.
2
Nodaviridae includes two
genuses: insect
Alphanodavirus
and fish
Betanodavirus
. The viral dis-
ease is found in many species of marine fish in Asia, Europe and
Australia. The symptoms of the diseased fish are described as viral
encephalopathy and retinopathy (VER), or viral nervous necrosis
(VNN), accompanied by syndromes of abnormal swimming behavior,
darkness of skin, and massive mortality in hatchery-reared larvae and
